Wave soldering is a bulk soldering process used to solder components to a printed circuit board. Solder is held in a wave soldering pot where the solder is heated and maintained in a molten state. The molten solder is pumped through a wave nozzle to form an up-welling of solder that appears as a standing wave. The printed circuit board is passed over the molten solder wave such that the component leads contact the molten solder.
An issue with the wave soldering device is that maintaining the solder in a molted state results in the formation of solder dross. Solder dross is a mass of impurities floating on the molten solder. The surface of the molten solder is exposed to air, and the solder dross is formed by oxidation of the molten solder.
Solder is an expensive material, but the solder dross is not useable due to the impurities. It is common practice to recycle the solder dross back to solder, which can then be reused. Different recycling techniques have been developed. One recycling technique is the periodic application of chemicals to the solder dross formed on the surface of the molten solder. The chemicals dissolve the oxides within the solder dross, however a resulting slag remains as waste. This slag must be periodically removed, typically by skimming. The slag is a messy material that may dirty other components of the wave soldering apparatus. Removing the slag is done manually, which is time consuming and costly, as well as dangerous since the molten solder is heated to at least 500 degrees Fahrenheit. The chemicals themselves are also costly and need to be periodically applied. Examples of such chemicals include a sodium hydroxide additive or a surfactant. A wave oil can also be used to reduce the formation of solder dross. The wave oil is applied to the surface of the molten solder and acts as a barrier between the molten solder and the atmosphere, thereby reducing oxidation and the formation of solder dross. However, wave oil does not completely eliminate the formation of solder dross, so the solder dross that does form still needs to be dealt with. The wave oil is also costly and needs to be periodically applied.
Another recycling technique is to physically separate the solder from the solder dross. In some cases, the solder dross is processed while still on the surface of the molten solder. This separation process can be as simple as using two stainless steel spatulas to squeeze the solder out from the solder dross. However, the safety and health of the operators is a concern considering the high temperature of the molten solder and the generation of harmful airborne particles during the separation process. In other cases, offline solder dross recovery machines are used. An operator needs to remove the solder dross from the wave soldering pot and place the recovered solder dross into a recovery pot in the offline solder dross recovery machine. However, during this transfer process the solder dross cools and hardens. For the machine to separate the solder from the solder dross, the solder dross must be heated to a molten temperature. This requires the machine to have a heater. Time is also required to melt the cooled solder dross. Also, not all solder is made of the same material, and therefore different offline solder dross recover machines are needed for different types of solder so as to avoid contamination. Good ventilation is also required during the operation.